RParser: include package system dependencies

[nokome]

We should use https://github.com/r-hub/sysreqs to install system dependencies for R packages.

See also:

• https://github.com/r-hub/sysreqsdb
• https://github.com/rstudio/shinyapps-package-dependencies

Additional, relevant discussions include:

• How to parse system dependencies ropensci/codemetar#147
• https://github.com/o2r-project/containerit/blob/master/vignettes/containerit.Rmd#7-challenges
• kindred project: sysreqs jlisic/sysdep#1

[nokome]

My initial attempt at using the sysreqs package failed e.g.

> sysreqs:::get_cran_sysreqs('XML')
NULL

compared to querying the database directly:

> http -b https://sysreqs.r-hub.io/pkg/XML
[
    {
        "libxml2": {
            "platforms": {
                "DEB": "libxml2-dev", 
                "OSX/brew": null, 
                "RPM": "libxml2-devel"
            }, 
            "sysreqs": "libxml2"
        }
    }
]

and the latter is more useful for integrating into the Node.js app in any case

[nokome]

Initial iteration of this done.